一天又一天（表示不知道未来会怎样），过一天算一天
before each day happens
I never know what I’ll be doing from one day to the next. 我从来不知道第二天会是什么样。
It's so unpredictable - you never know what you're going to find from one day to the next.
It's so strange how your feelings about the same situation can change from one day to the next.
I have no idea how she'll be from one day to the next.
See also: day